1. Field of the Invention
The present invention relates to a liquid crystal display device which includes a backlight for illuminating a liquid crystal panel (for displaying images) from behind and executes brightness adjustment of the backlight according to an image signal inputted for the displaying of the images.
2. Description of the Related Art
A liquid crystal display device is equipped with a non-emitting liquid crystal panel (light-transmissive optical modulation element) and a backlight arranged behind the liquid crystal panel to illuminate the panel with light, differently from self-emission display devices (CRT, plasma display panel, etc.). In general, the liquid crystal display device displays images at desired brightness by controlling the optical transmittance of the liquid crystal panel according to the brightness specified by the image signal while making the backlight emit light at a fixed brightness level irrespective of the image signal. Therefore, the electric power consumption of the backlight remains constant without decreasing even when dark images are displayed. This leads to low electric power efficiency of the liquid crystal display device. A technique proposed as a countermeasure against this problem employs variable brightness of the backlight. The technique reduces the electric power consumption while improving the image quality, by controlling the grayscale level of the liquid crystal panel and the brightness of the backlight according to the brightness level (luminance level) of the inputted image signal. There also exists a technique known as “area control” or “local dimming”, in which the backlight is segmented into multiple areas and the backlight brightness control is conducted for each of the areas.
For example, in a liquid crystal display device described in the first embodiment of JP-A-2008-15430, the backlight is segmented into a plurality of areas, the brightest grayscale level in each area in one frame of the inputted image signal is detected in regard to each primary color (R, G, B), and the grayscale levels of the inputted image signal are converted (adjusted) so that the brightest grayscale level equals the upper limit of the grayscale level, while making the backlight blink (at a high frequency) at a duty ratio corresponding to the ratio of the detected brightest grayscale level to the upper limit of the grayscale level during the lighting period of the backlight.